1. Field of the Invention
The present invention relates to a magnetoresistive element (hereafter referred to as an MR element), a thin film magnetic head and a method for manufacturing thereof.
2. Description of the Prior Art
As the current demand dictates a trend for miniaturization of magnetic disk drive apparatuses, thin film magnetic heads that employ an MR element as a read element are known in the prior art as magnetic converters that are suited for reading information stored on a magnetic recording medium at a high recording density since the output is not dependent upon its speed relative to the magnetic disk.
An example of a magnetic conversion element employed in a thin film magnetic head is disclosed in Japanese Unexamined Patent Publication No.125311/1991. The magnetoresistive reader disclosed in this publication is provided with a central active area and a pair of passive areas. The central active area includes a magnetoresistive film (hereafter referred to as an MR film), a non-magnetic film and a soft magnetic film, with the soft magnetic film imparting a lateral bias to the MR film. The pair of passive areas each include a magnetic domain control film and a conductive film. The magnetic domain control films are laminated at the two ends of the central active area facing opposite each other over a distance with the conductive films provided on top of the magnetic domain control films.
The soft magnetic film included in the central active area applies a lateral bias to the MR film, thereby assuring linear operation when reading magnetically recorded data. When the magnetic field generated from the magnetically recorded data on the magnetic recording medium is applied to the MR film in the direction intersecting the direction of magnetization of the MR film, the direction of magnetization of the MR film changes. Thus, the resistance value of the MR film changes in correspondence to the change in the direction of magnetization, resulting in a sense current corresponding to the magnetically recorded data. Since, when the magnetic field generated from the magnetically recorded data on the magnetic recording medium matches the direction of magnetization of the MR film, the direction of magnetization does not change and the resistance value of the MR film does not change significantly.
The magnetic domain control films are provided to prevent Barkhausen noise by applying a longitudinal bias to the MR film. U.S. Pat. No. 4,024,489 discloses an MR sensor that employs a hard magnetic bias film as a magnetic domain control film.
In the MR element described above, since no lateral bias is applied due to the strong longitudinal bias applied by the magnetic domain control film in the vicinity of the areas where the magnetic domain control films contact the MR film, dead zones are formed.
A dead zone does not function as a sensor and increases the electrical resistance value in the magnetoresistive sensor circuit. If the electrical resistance at the magnetoresistive sensor circuit increases, its performance as a magnetoresistive sensor circuit is degraded. Furthermore, the risk of electromigration occuring due to high density current increases.
As a means for reducing the electrical resistance value, which increases because of the dead zones, conductive films are provided adjoining the central active area at both sides beyond the dead zones. Since dead zones are formed uniformly at the two side ends of the MR film, it is necessary to form the conductive films uniformly at the edges of the MR film at the two sides. Without such uniformity, the electrical resistance value will still increase due to the non-operating areas and the magnetic reliability of the MR film under the conductive films, which is operable, will deteriorate.
U.S. Pat. No. 5,438,470 discloses a structure achieved by placing only a conductive film on the central active area and a structure achieved by placing a magnetic domain control film and a conductive film over areas of equal dimensions on the central active area. However, in the structure achieved by placing only the conductive film over the central active area, a difficulty of accurately aligning the side end surface of the magnetic domain control film with the side end surfaces of the central active area must be overcome in production. In addition, the structure achieved by placing the magnetic domain control film and the conductive film over areas of equal dimensions on the central active area poses the problem discussed in the reference to patent specification cited earlier.
Furthermore, U.S. Pat. No. 5,438,470 discloses a structure in which uniformity is achieved at the two edges of the MR film in the degree to which the conductive films overlap at the two ends of the central active area. However, in the patent no mention is made as to the specific means for achieving uniformity for the overlapping dimensions of the conductive films.